In this report the results are summarized of measurements concerning the influence of intermolecular hydrogen bridge formation on the mechanisms responsible for the so-called p- and y-relaxations in the dielectric loss spectrum of nylon 6.6’) (see McCrum et al.’, p. 478497). To that end the loss spectra and the IR carbonyl absorptions in the range from 1 500 to 1 700 cm - were studied of polyester 6.6**)a nd of nylon 6.6, modified by partly substitution of amide-hydrogen by methyl or ethyl groups. This work is intended to give a contribution to the elucidation of the still existing controversy2- s, concerning the mechanisms mentioned above. Up till now, the idea of Woodward et aL6) of N-substitution as a tool in the interpretation of these secondary transitions in the dielectric loss spectrum of nylon 6.6, was not pursued further.